AN EQUATION FOR DEVELOPING MULTI-CAUSAL EXPLANATIONS FOR CHANGES IN BIODIVERSITY

Most efforts to understand the cause(s) of diversity change observed in the fossil record focus on specific time intervals, usually those characterized by major origination or extinction events.  Here, rather than focusing on a specific event or time interval, I develop a framework that should be useful for understanding the general controls on changes in biodiversity.  The first step consists of listing the factors that must be important in controlling total diversity.  These factors include:  total habitable surface area (A); the total amount of usable energy entering the ecosystem (E); extrinsic barriers to gene flow between populations, such as oceans, mountain ranges, rivers, etc. (B_ex);  intrinsic barriers to gene flow between populations (B_in);  and, the "Darwin factor", the complex relationship between the genetic potential for morphological and behavioral innovation (governed by morphogenetic rules, M), the tasks (T) the organisms needs to perform to leave viable offspring, and the biotic (E_b) and abiotic (E_ab) environments.  The Darwin factor can be visualized using fitness landscapes, and changes in diversity under the control of this factor may occur by:  increasing the fitness landscape's dimensionality (adding morphogenetic rules); increasing the size of one or more dimensions (by increasing the repertoire of the morphogenetic rules); changing the roughness of the landscape (changing the number of needs that each species must meet to pass its genes onto the next generation), and/or through changing of the minimum viable fitness (the "sea-level") on the landscape, either through environmental change, or evolutionary escalation.  While it is all but impossible to quantify the importance of each factor at even given time, it may be possible, using the geological record and through functional and ecological analysis of the morphology of the taxa involved, to determine which factors are most important at times when diversity changes.  This framework is flexible enough that complex interactions and casual cascades can be diagrammed, and so offers an opportunity for developing a general theory of biodiversity change that can accommodate multi-causal hypotheses.